1. Field of the Invention
The present invention relates to an antireflection film forming composition, more specifically, to a composition for forming a low-refractive-index film having an adequately uniform thickness and useful as an antireflection film or the like in optical devices, an antireflection film and an optical device.
2. Description of the Related Art
Antireflection films have been used for preventing reflection of an outside light and enhancing an image quality during laser annealing or in a photoresist step for producing various display panels such as liquid crystal display panel, cold cathode fluorescent lamp panel and plasma display, solar cell panels, optical devices such as imaging element, thin film transistors, and thin-film single-crystal silicon solar cells.
Based on the optical theory of antireflection, antireflection films are classified into those made of a plurality of layers obtained by stacking on a substrate a high-refractive-index layer made of a metal oxide or the like and a low-refractive-index layer one after another and those made of a single layer having only a low-refractive-index layer made of an organic fluorine compound or an inorganic compound. In either type of antireflection films, there is a demand for the development of a low-refractive-index material made of a cured film excellent in scratch resistance, coating properties, and durability.
A method of employing dehydration condensation of a siloxane compound or forming pores by using a thermally decomposable compound is known as a method for producing a material having a lower refractive index. Such a method however poses problems such film shrinkage and degassing during baking.
An attempt to obtain a low-refractive-index film by applying a solution obtained by adding a low-molecular cage-type siloxane compound to an organic polymer is also known (refer to Japanese Patent Laid-Open No. 2000-334881). The method of adding a cage-type compound as a monomer is not sufficiently effective for reducing a refractive index and in addition, has problems such as worsening of a coated surface and large film thickness loss during baking.